Medical Microbiology

Malarialparasitescanbetransmittedbyfemalemosquitoesofabout 80

speciesofthegenusAnopheles(Anophelesgambiaecomplex,etc.).Thelarval

andpupalstagesofthesemosquitoesdevelopinstandingbodiesofwater,

oftennearhumandwellings.Anophelinemosquitoesareactivefromdusk

todawn.Thefemalesbitebothintheoutsideandwithinbuildings.Malaria

oftenaccompaniestherainyseason,whichprovidesthebodiesofwaterthe

mosquitoesneed.Occurrenceisusuallyendemic,butepidemicsdosome-

timesdevelop.Theincidenceofinfectionsvarieswidelyandtheimmunesta-

tusofthepopulationisamajorfactor(seeimmunityp.530).

Alternativetransmissionroutesformalarialplasmodiaincludediaplacen-

talinfection,bloodtransfusions(plasmodiasurviveinstoredbloodforfive

days,rarelylonger),andcontaminatedneedlesusedbydrugaddicts.

Diagnosis.Etiologicalconfirmationofaclinicaldiagnosisisobtainedbyde-

tectingmalarialparasitesintheblood(Fig.9. 18 ).Capillarybloodissampled

beforechemotherapyisstarted,ifpossiblebeforetheonsetoffever,andex-

aminedmicroscopicallyinboththickandthinbloodsmearsfollowingGiem-

sastaining(p.622).StagesofP.falciparum,P.vivax,andP.ovalecanbefound

inbloodfivetoeightdaysaftertheinfectionattheearliest,P.malariaenot

untilafter 13 – 16 days.TheQBC(quantitativebuffycoat)methodcanbeused

toconcentratetheplasmodia.Rapidtests(ParaSight,MalaQuick)havealso

beenavailableforsomeyearstodiagnoseP.falciparuminfections.Usinga

monoclonalantibody,thesetestscandetectaspecificPlasmodiumantigen

(HRP2)inwholebloodwithaveryhighlevelofsensitivityandspecificity.

Anotherrapidtest(OptiMAL)fordiagnosisofallPlasmodiumspeciesisbased

ondetectionofspecificlactatedehydrogenase.

Detectionofspecificantibodiesintheserumofpersonsinfectedwith

plasmodiaforthefirsttimeisnotpossibleuntilsixto 10 daysafterinocula-

tion(Table 11. 5 ,p.625).Insuchcases,aserologicalantibodyassayisnota

suitabletooltoconfirmadiagnosisinanacuteattackofmalaria,although

thismethoddoesprovidevaluablehelpinconfirmingolderinfectionsand

screeningoutblooddonorsinfectedwithplasmodia.DNAdetectionby

meansofPCRcanbeusedtoidentifythedifferentPlasmodiumspeciesfor

researchpurposes.

Therapy.Patientsinfectedforthefirsttime(e.g.,travelersfromthenorthern

hemispherereturningfromastayinthetropics)maysufferhighlyacuteand

severecoursesofmalaria.Therapyandintensiveclinicalmonitoringmust

thereforebeginimmediately,especiallyinacutemalignanttertianmalaria

(malariatropica)(medicalemergency!).Table9. 6 summarizesanumber

ofantimalarialsandtheirspectraofaction.Thebestthatcanbeoffered

herebywayofadescriptionofthehighlycomplexfieldofmalariatreatment

isabriefsketchofthemainprinciplesinvolved.

Plasmodium 531

9

Kayser, Medical Microbiology © 2005 Thieme